The present invention relates generally to a method of color correction of liquid crystal display (LCD) projection or direct view displays and, more particularly, to controlling the throughput of two different color channels to control the white point of a projector.
Many different colors are specified as xe2x80x9cwhitexe2x80x9d in both video and monitor systems. For example, in cinema work 5400K is specified as xe2x80x9cwhitexe2x80x9d, but in video work 6550K is specified as xe2x80x9cwhitexe2x80x9d. Ranges from 3800K to 9300K are used to specify xe2x80x9cwhitexe2x80x9d in other applications. Therefore, to enable an end user to accurately judge the color of the finished product which appears on a monitor, it is necessary to adjust the monitor xe2x80x9cwhitexe2x80x9d point to the xe2x80x9cwhitexe2x80x9d point specified for that particular application.
In CRT monitors, the specified xe2x80x9cwhitexe2x80x9d point can be attained by adjusting the relative gains of the red, green and blue video amplifiers so that when all three video signals (R, G and B) are equal, the desired target xe2x80x9cwhitexe2x80x9d is displayed. Changing the xe2x80x9cwhitexe2x80x9d point in such a system can be effected by changing the relative gain of the red, green and blue amplifiers. This manner of attaining the specified xe2x80x9cwhitexe2x80x9d point, however, has several disadvantages when it is incorporated in an LCD display. If the requisite gain is effected in the analog domain, the change not only effects the xe2x80x9cwhitexe2x80x9d point, but effects all other colors as well. Accordingly, modified gamma correction curves are then required for each target xe2x80x9cwhitexe2x80x9d point. If the gain adjustment is effected in the digital domain, some of the dynamic range must be ignored and not used. Because eight bits is generally considered the minimum number of bits required for effective color display, disregarding portions of the dynamic range will generally lead to serious color artifacts. Even with greater basic resolution, ten or twelve bits, color artifacts can result when interpolating the video signal to a smaller dynamic range.
Therefore, while these methods previously described are suitable for use in color correction for devices such as CRT monitors, these methods are not suitable for adjusting the color of a projection or direct view LCD display.
Using a fixed and variable retarder to correct color temperature, referred to as one dimensional correction, results in changing the color of the light in the illumination path. This does not permit the xe2x80x9cwhitexe2x80x9d point to be fully adjustable, limiting the adjustment to one dimension along the black body line. Accordingly, if the starting or target xe2x80x9cwhitexe2x80x9d point is not on the black body line complete adjustment of the xe2x80x9cwhitexe2x80x9d point is not possible.
Changing the relative intensity of the red, green and blue color channels, such as through the use of a ColorLink polarizer, to control the amount of light in all three R, G and B channels to reach the target xe2x80x9cwhitexe2x80x9d point over-controls the xe2x80x9cwhitexe2x80x9d point. Color space is a two-dimensional space, commonly designated x-y color coordinates. The third coordinate in this system is the brightness coordinate. Brightness does not play a role in xe2x80x9cwhitexe2x80x9d point correction. Accordingly, only a two dimensional color correction system is necessary to fully control the xe2x80x9cwhitexe2x80x9d point of an LCD display.
The present invention is directed to overcoming one or more of the problems or disadvantages associated with the relevant technology.
In the preferred embodiment of this invention, the color of a projection or direct view LCD display may be adjusted without changing the input video signal in either the analog or digital domains. Accordingly, color adjustment is effected optically and is controllable while the projector is operating. In this manner, a fully adjustable xe2x80x9cwhitexe2x80x9d point is attained which is not limited to adjustments along the black body line. In the preferred embodiment, the throughput of two different color channels is used to control the xe2x80x9cwhitexe2x80x9d point of a projection display thereby effecting two-dimensional color corrections. Partially polarized light produced by an integrator/polarization conversion system combination and two non-pixilated twisted nematic liquid crystal display cells (TN-LCD) or other light modulators are utilized. By adjusting the voltages on the TN-LCD cells, it is possible to adjust the relative amounts of the greatest two of the colors supplied, of the red, green and blue colors, used by the display without changing the light of the color in the least supply. Because all of the adjustments are done electronically through voltage controls, not mechanically, the xe2x80x9cwhitexe2x80x9d point correction system is both simple and reliable. Electronic adjustment can also easily accommodate changing end user xe2x80x9cwhitexe2x80x9d point requirements.